Biazzi Renata B, Takahashi Daniel Y, Ghazanfar Asif A
bioRxiv. 2024 Oct 29:2024.10.29.620895. doi: 10.1101/2024.10.29.620895.
Human infant vocal development is strongly influenced by interactions with caregivers who reinforce more speech-like sounds. This trajectory of vocal development in humans is radically different from those of our close phylogenetic relatives, Old World monkeys and apes. In these primates most closely related to humans on the evolutionary tree, social feedback plays no significant role in their vocal development. Oddly, infant marmoset monkeys, a more distantly related New World primate, do exhibit socially guided vocal learning. To explore what developmental mechanism could have evolved to account for these behavioral differences, we hypothesized that the evolution of human and marmoset vocal learning in early infancy in both species is because they are born neurally altricial relative to other primate and in a cooperative breeding social environment. Our analysis found that, indeed, human and marmoset brain are growing faster at birth when compared with chimpanzees and rhesus macaques, making them altricial relative to these primates. We formalized our hypothesis using a logistic growth model showing that the maturation of a system dependent on the rate of brain growth and the amount of social stimuli benefits from an altricial brain and a cooperative breeding environment. Our data suggest that in primates, the evolution of socially guided vocal learning during early infancy in humans and marmosets was afforded by infants with a relatively altricial brain and behavior, sustained and stimulated by cooperative breeding environments.
Humans rely on social feedback from caregivers to learn how to produce species-typical sounds, whereas other primates like macaque monkeys or chimpanzees do not. What accounts for this difference in developmental strategies? We tested the hypothesis that being born with a more immature (thus more plastic) brain may be the reason by using marmoset monkeys. This species is more distantly related to humans but exhibit the same type of vocal learning and who have a similar socially rich infant care environment. We found that, indeed, human and marmoset brain are growing faster at birth when compared with chimpanzees and rhesus macaques, making them altricial relative to these primates and this explains their similar vocal developmental strategies.
人类婴儿的发声发展受到与照顾者互动的强烈影响，照顾者会强化更多类似语音的声音。人类这种发声发展轨迹与我们在系统发育上的近亲——旧世界猴和猿类截然不同。在进化树上与人类关系最为密切的这些灵长类动物中，社会反馈在它们的发声发展中不起重要作用。奇怪的是，婴猴作为一种亲缘关系更远的新世界灵长类动物，确实表现出社会引导的发声学习。为了探究可能进化出了何种发育机制来解释这些行为差异，我们推测人类和婴猴在婴儿早期发声学习的进化是因为它们相对于其他灵长类动物在出生时神经发育不全，且处于合作繁殖的社会环境中。我们的分析发现，事实上，与黑猩猩和恒河猴相比，人类和婴猴的大脑在出生时生长得更快，这使得它们相对于这些灵长类动物而言神经发育不全。我们使用逻辑增长模型将我们的假设形式化，结果表明，一个依赖于大脑生长速度和社会刺激量的系统的成熟受益于神经发育不全的大脑和合作繁殖的环境。我们的数据表明，在灵长类动物中，人类和婴猴在婴儿早期社会引导的发声学习的进化是由大脑和行为相对神经发育不全的婴儿实现的，这种进化由合作繁殖环境所维持和刺激。
人类依靠照顾者的社会反馈来学习如何发出物种特有的声音，而猕猴或黑猩猩等其他灵长类动物则不然。这种发育策略的差异是由什么造成的？我们通过使用婴猴来测试这一假设，即出生时大脑更不成熟（因而更具可塑性）可能是原因所在。这种物种与人类的亲缘关系更远，但表现出相同类型的发声学习，并且拥有类似的社会丰富的婴儿照料环境。我们发现，事实上，与黑猩猩和恒河猴相比，人类和婴猴的大脑在出生时生长得更快，这使得它们相对于这些灵长类动物而言神经发育不全，这也解释了它们相似的发声发展策略。
